There is conventionally known a device equipped with a phase changing mechanism for linking a sprocket rotating in association with a drive shaft to a lever member rotating in association with a driven shaft through a link arm. This kind of a phase changing mechanism is arranged to convert a motion of the link arm into a relative rotational motion of the lever member to the sprocket, thereby changing a relative rotational phase between the drive shaft and the driven shaft.
JP-200548707A, for instance, discloses technology for defining a changing angle of a relative rotational phase in a relative rotational motion of a cam plate (link part) as a lever member. In this technology, two stoppers are provided in a sprocket for restricting a position of the relative rotational phase of the cam plate. At a phase position where the rotational phase of the cam plate is at the most advance angle, the cam plate contacts an advance-side stopper, and on the other hand, at a phase position where the cam plate is at the most retard angle, the cam plate contacts a retard-side stopper. Contact between the stoppers and the cam plate defines a changing angle of the relative rotational phase between the drive shaft and the driven shaft.
The cam plate can collide with the stoppers at relatively high force. For instance, where a predetermined motion of the link arm and the cam plate is created by transmission of a rotational motion by an electric motor, and when power supply to the electric motor is stopped, the stoppers can experience a relatively large collision torque.
In partial response to this problem, an elastic member can be provided at the stopper with which the cam plate collides. As such, it is possible to alleviate the effect of the impact by interposing the elastic member between the cam plate and the stopper. However, since elastic response of the elastic member can change with a magnitude of the impact force, the phase position where the cam plate becomes the most retard angle can shift, which can adversely influence learning of the most retard angle.